This invention relates to the field of electric power transmission and more particularly to flexibly coupling a transportable consumer to a stationary power network, using an electric multiconductor cable.
Flexible electric cables which are used for the control and/or power supply of transportable consumers such as lifting devices, transporting and conveyer installations, and which are continuously wound on and unwound from a drum, are subjected to considerable mechanical stresses. Sometimes, these stresses lead to corkscrew-like dislocations of a cable. In itself, the design of such a cable which consists in the usual manner of insulated conductors twisted with each other or about a core (dummy conductor or supporting member) and of a one or two layer jacket, which is optionally provided with an embedded braid and, sometimes, a filling of the corners between the insulated conductors, which takes the occurring mechanical stresses into account is known. (DE-OS No. 25 04 555). Even with the disclosed design, mechanical stresses can result from torsional and tensile stresses of the insulated conductors in conjunction with their mobility relative to each other as well as relative to the jacket, which result in the mentioned dislocations.
For controlling the internal stresses in a cable that can be wound on a drum, a design is known, in which each insulated conductor is surrounded by a hose-like, extruded synthetic material layer with the interposition of a release agent layer containing a lubricant, and in which this hose layer is connected with material contact to the core and/or the jacket. In such a cable, the core, the hose-like plastic layer of the insulated conductors and the inner jacket form an elastic, flexible corset, in which the insulated conductors can move independently of each other with a sliding motion. Because of the material locking connection of several design elements which are distributed over the cross section, the flexibility of the cable as a whole is impeded (DE-OS No. 31 51 234).
For the power supply of mining equipment, a cable, in which, in the corner spaces of the mutually twisted insulated conductors, the ground conductor, as well as corner fillings of rubber-like material, are arranged and in which the twisted conductors are surrounded by a jacket provided with a reinforcement braid and a wrapping applied with a counter-lay, has been developed (U.S. Pat. No. 3,699,238).
For the mechanical design of control cables with layer-wise twisted insulated conductors, it is further known to arrange, in the corners between the conductors, a sliding agent in powder form as well as dust-tight release layers between the individual twisting layers (Swiss Pat. No. 389,047) or to provide, with the same twist direction in all twisting layers, for each twisting layer, a tape wrapping, the pitch direction of which is opposite to the twist direction of the twisting layers (DE-AS No. 14 65 777).
Starting out with a multiconductor flexible electric cable of the type described in U.S. Pat. No. 3,699,238, it is an object of the present invention to improve by design measures the control of the internal stresses occurring in winding and unwinding on or from a drum, without thereby affecting the flexibility of the cable adversely.